Engineering Electronic Radial Effects for Fast Li⁺ Transport in Solid-State Electrolytes

Area of Science:

• Materials Science
• Electrochemistry
• Solid-State Chemistry

Background:

• Solid-state electrolytes are crucial for advanced lithium-metal batteries but face challenges in achieving high ionic conductivity, transference numbers, and interface stability.
• Current electrolyte designs struggle to balance these critical properties, hindering the development of next-generation energy storage.

Purpose of the Study:

• To introduce a novel radial-effect design principle for solid-state electrolytes.
• To leverage relativistic effects and machine learning for discovering new electrolyte materials.
• To engineer high-performance, thermally resilient solid-state batteries.

Main Methods:

• Introduced a radial-effect design principle involving relativistic expansion and spin-orbit coupling of 5d orbitals.
• Developed an entropy-based descriptor (S_d) trained with machine learning across over 10,000 materials.
• Utilized machine-learning-guided high-throughput screening to identify monoclinic HfO₂.
• Employed millisecond flash-Joule heating to synthesize nanosized HfO₂ crystals.
• Fabricated sc-HfO₂@LCB composite electrolytes and assembled lithium-metal pouch cells.

Main Results:

• Radial-effect engineering in HfO₂ significantly lowered Li⁺ migration barriers.
• The sc-HfO₂@LCB electrolyte exhibited high Li⁺ conductivity (1.23 mS cm^-1 at 30°C) and transference numbers (t_{Li +} = 0.82 at 25°C).
• Achieved a wide electrochemical window (4.8 V) and confirmed faster Li⁺ transport via operando Raman/XANES.
• Demonstrated superior performance in 2 Ah LiNi_0.9Co_0.05Mn_0.05O₂‖Li pouch cells, reaching ~472 Wh kg^-1 (stack-level) and maintaining rate capability over hundreds of cycles.
• Cells survived 150°C hot-plate tests, indicating enhanced thermal resilience.

Conclusions:

• Radial-effect engineering is a powerful strategy for designing advanced solid-state electrolytes.
• The developed HfO₂-based electrolyte offers a promising pathway towards high-performance, safe, and thermally stable lithium-metal batteries.
• This approach enables the creation of interconnected Li⁺ pathways, crucial for efficient ion transport.